The present invention relates to a solar heater, particularly a solar heater in which there are multiple parallel flow channels for a heat-carrying medium any two adjacent ones of which flow channels have a common linear divider, with at least some of the dividers terminating short of an edge of the solar heater, and in which there are inlet and outlet conduits which communicate with the interior of the heater for allowing heat-carrying medium, as, for example, water, to be introduced into and to flow out of the flow channels. Such a solar heater may be made of two superposed layers of foil material which are fluid-tightly joined to each other along their edges as well as along straight lines, these fluid-tight, straight line joints constituting the dividers so as to form flow channels which are bounded by the two layers and by consecutive dividers. In practice, the two layers may be portions of a single strip of foil material which is folded over so that the two opposite portions of the single strip overlie each other and thus form the two layers, respectively.
A solar heater of the above type is shown, for example, in U.S. Pat. No. 3,022,781, in which the flow channels form a meander-shaped flow path, this being achieved by letting consecutive dividers start out from opposite edges of the mat-shaped solar heater, with each divider terminating short of the other edge, so that there is a comb-like interlacing of the dividers. The inlet and outlet conduits, which may be constituted by plastic tubes, communicate with the two outermost flow channels. In practice, of course, the dividers may terminate short of both edges of the solar heater, so that the flow channels are connected in parallel such that the medium may flow simultaneously from the inlet conduit to a common inlet header and from there through each of the individual flow channels, which thus form parallel flow paths, to a common outlet header and thence to the outlet conduit.
Mat-shaped solar heaters of the above type have the advantage over solar heaters which are made of rigid parts, such as metal plates, that they can be rolled up and thus easily transported. If such a heater is used, for example, for heating a swimming pool, the heater can easily be removed when no heating is required or if the pool is closed. Moreover, the rolled up heater takes up relatively little space so that it can be conveniently stored.
The above advantages notwithstanding, it has been found that mat-like solar heaters of the above-described general type have the drawback that it is difficult to remove all of the water or other heat-carrying medium from the interior of the flow channels. This is so because when there is a less than atmospheric pressure in the flow channels, the foils which form the outside walls of the flow channels will come to lie against each other and even tend to adhere to each other, so that water is trapped within the flow channels, thus making it difficult to empty the flow channels completely.
It is, therefore, the primary object of the present invention to provide a mat-shaped solar heater of the above-described general type which, when it is no longer needed, can easily and quickly be emptied of water or other heat-carrying medium.